A problem with some existing exercise apparatus is that there is little control over the direction and/or loading on the joints throughout the range of motion of the exercise.
Non-cam based fixed weight machines, free weights and cable machines, for example, are capable of training multiple joints, but provide a load that is fixed in a particular direction, which is defined by the direction of gravity, direction of the cable, and/or the movement of the mechanism; the load direction does not adjust with the user's movements. Therefore, as the user moves their limb, for example, the load might initially act perpendicularly to the motion but during the range of movement, the load acts at an angle away from perpendicular.
As a result, the, or each, joint is not fully loaded, thereby reducing the efficiency of the exercise. Additionally, because the user's joints are not supported with cable machines and free-weights, the user can be exercising using poor form, especially when tired, which may damage the joint and/or muscles.
Cam based machines, such as those made by Nautilus, load joints evenly throughout their range of motion using rotational loading applied at the joint by a cam. Such machines have been available for some time. A disadvantage of such machines is that they are restricted to one joint being exercised in one direction; only a single joint is exercised and multi-articular exercises are not possible.
U.S. Pat. No. 7,645,216 B2, in the name of William Kurt Edeker, discloses exercise machines that comprise pivoting parts comprising linked cam arrangements that allow for multi-joint exercises. One disadvantage of these machines is that they only operate in a single plane of motion and/or path of movement. A further disadvantage is that because the cams are linked, the parts that pivot to exercise the joints are dependently linked such that movement of one part induces or depends upon movement of another. By being dependently linked, the benefit of the machine on each joint is limited because a larger muscle group may compensate for a smaller muscle group, thereby reducing the effectiveness of the exercise. Furthermore, such training does not provide a load on the whole range of movement of at least one of the joints.
WO2008009949 (A1) discloses muscle conditioning apparatus for strengthening a user's cervical spine. However, its movement is limited to allow exercising of the back and the neck only.